Mitigating the Effects of Chytridiomycosis

For the last couple of years our research group has conducted several field experiments aimed at understanding the extent to which we can change the outcome of outbreaks of the amphibian chytrid fungus (Batrachochytrium dendrobatidis - "Bd") from frog population extinction to persistence. This summer and last we treated frogs at die-off sites with anti-fungal drugs, something I never in my wildest nightmares imagined that I'd ever be doing. My field crews and I put everything we had into those experiments but so far success remains elusive. 

Given our attempts at changing disease outcomes I was excited to attend a disease mitigation workshop last week in Zurich, Switzerland and learn what other researchers from around the world have been trying. Over a two day period we learned of each others myriad efforts to confront the Bd plague and were sobered to realize that all of the attempts at changing Bd disease outcomes attempted so far have failed. 

At a Bd-positive site in Mallorca (Spain) Jaime Bosch and his colleagues removed all of the amphibians, treated them in the laboratory with an anti-fungal drug until they were Bd-free, and then completely dried the pond. When winter rains refilled the pond the treated tadpoles were released back into the site. Much to everyone's surprise by spring the tadpoles were once again infected with Bd. Given that Bd apparently does not have a resistant stage that could survive dessication it remains a mystery how Bd survived at the site or reinvaded so quickly (additional details are provided here). 

A graduate student at the University of Zurich, Corina Geiger, recently conducted an experiment in which she established frog populations in large outdoor tanks which she subsequently infected with Bd. Once the frogs showed evidence of chytridiomycosis she treated the entire tanks with antifungal drugs. For six weeks following treatment frogs were uninfected, but then Bd reappeared and reinfected the frogs. These results mirror our own results to date in the Sierra Nevada. 

Other mitigation efforts are currently ongoing, including an experiment using frog skin bacteria that have strong anti-Bd properties (additional details provided here), and another in which amphibian densities are being temporarily reduced to assess the effect on disease dynamics.

The ineffectiveness of the anti-Bd treatments attempted to date is obviously disappointing and illustrates just how incomplete our understanding of Bd still is. If we do stumble across an effective mitigation strategy it seems it will be almost entirely a stroke of luck. And yet, with Bd spreading into new uninfected populations with every passing month, we don't have the luxury of waiting for better information.

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